A process in which a liquid surfactant such as a nonionic surfactant is used for a powder detergent includes a process of supporting a liquid surfactant on a powder.
Japanese Patent Laid-Open No. Sho 52-110710 discloses a granular detergent comprising a liquid or liquefiable organic substance contained in an inner portion of base material beads having porous outer surface and skeletal inner structure, wherein a nonionic surfactant is not substantially present on the beads surface. However, in this technique, the beads cannot include liquid ingredients in amounts of not less than an oil-absorbable amount, and moreover, liquids are more likely to remain on the particle surface as the amount of the surfactant formulated increases, thereby making its flowability poor. Therefore, the amount of the surfactant formulated by this technique cannot be increased.
Japanese Patent Laid-Open No. Hei 5-209200 discloses a process for preparing a nonionic detergent particle, comprising using, as raw materials for detergents, a mixture comprising a nonionic surfactant as a main base material; forming a deposition layer of the raw materials for detergents on a wall of an agitation mixer comprising agitation impellers and having a clearance between the agitation impellers and the mixer wall; and granulating with increasing a bulk density by the agitation impellers. However, in this technique, the process is complicated, and as the amount of a surfactant formulated varies, the particle size of the detergent particle varies. Further, in this technique, as a matter of course, the deposition of the raw materials for detergents in the mixer is remarkable, which may cause variations in the particle size and the bulk density of the detergent particle depending upon the deposition conditions.
Further, Japanese Patent Laid-Open No. Hei 10-176200 discloses a process for preparing nonionic detergent granules comprising previously mixing a nonionic surfactant, a water-soluble, nonionic, organic compound having a melting point of 45° C. or more, and an acid precursor of a fatty acid or the like, to give a liquid mixture; and granulating a mixture of the resulting liquid mixture with raw materials for detergents, with tumbling with an agitation mixer, thereby increasing its bulk density. However, the fatty acid reacts in the nonionic surfactant by contacting the liquid mixture with an alkalizing agent, thereby causing gelation (nonionic surfactant/soap gel). Therefore, the surfactant composition comprising a nonionic surfactant is less likely be absorbed and embedded in powder raw materials having supporting ability, and the powder raw materials are aggregated with the gelated product acting as a binder, whereby the granulation proceeds. In other words, in the above process, the granulation proceeds without sufficiently exhibiting its supporting ability, even when using powder raw materials having supporting ability in the powder raw materials, so that a large amount of the surfactant cannot be formulated. When a large amount of the surfactant is to be formulated, granules having sizes outside of the desired particle size ranges are formed, so that it tends to be disadvantageous in the dissolubility.
Therefore, in order to produce products having stable quality, it is very important to construct a process for preparing powder detergents for obtaining products having stable quality with respect to the variation in the amount of the nonionic surfactant formulated. Especially, although a powder detergent having a high liquid surfactant content is excellent in the deterging performance, it has been difficult to produce a product having stable quality for the reasons given above, and the problem of adversely changing powder properties by containing a large amount thereof has not been solved thereby.
Accordingly, a first object of the present invention is to provide in a process for preparing detergent particles comprising a surfactant composition, the process for obtaining detergent particles in high yield capable of easily adjusting an average particle size and a particle size distribution by selection of base particles in a simple preparation process, wherein the variations of the average particle size and the particle size distribution of the detergent particles are small with respect to the variation of the amount of the surfactant composition formulated. Further, a second object of the present invention is to provide a process for preparing detergent particles which are excellent in powder properties, such as flowability, of the detergent particles, and are capable of formulating a large amount of the surfactant composition. Further, a third object of the present invention is to provide in a process for preparing detergent particles comprising a nonionic surfactant, the process for preparing detergent particles having a large surfactant content in a simple preparation process, excellent dissolubility, and being excellent in the suppression of exudation of the nonionic surfactant and in the anti-caking property. These objects and other objects of the present invention will be apparent from the following description.